Dracunculiasis — DTM&H MCQ

Correct answer: B — Freshwater copepod

The correct answer is B, freshwater copepod. Dracunculus medinensis (Guinea worm) is acquired when people drink unfiltered stagnant water containing copepods infected with the L3 larvae, and the classic clinical picture of a painful blister on the lower leg with a white worm slowly emerging after bathing is pathognomonic for dracunculiasis. As the WHO fact sheet states, dracunculiasis is transmitted when people swallow water contaminated with parasite-infected water fleas (cyclops), and once the adult female worm reaches the skin a year later, immersion in water triggers larval release, perpetuating the cycle. The stem's emphasis on unfiltered surface water and the pond-bathing history is the key epidemiological clue pointing to the copepod as intermediate host rather than an insect vector. Why the other options are wrong: C. Phlebotomine sandfly: this is the vector for leishmaniasis, transmitting Leishmania via a bite, not ingestion of contaminated water, and does not cause a slowly emerging worm. E. Bulinus snail: this snail is the intermediate host for Schistosoma haematobium, which causes haematuria and bladder disease via skin penetration by cercariae, not a leg blister with an emergent worm. A. Triatomine bug: this reduviid bug transmits Trypanosoma cruzi (Chagas disease) through faecal contamination of a bite wound, unrelated to waterborne transmission or worm emergence. D. Simulium blackfly: this is the vector for Onchocerca volvulus (onchocerciasis), causing skin nodules and river blindness via bites near fast-flowing rivers, not stagnant pond water ingestion. Key point: A painful lower leg blister with a slowly emerging white worm after bathing in stagnant, unfiltered water is classic for Guinea worm disease, acquired by swallowing water containing infected copepods.

Reference: World Health Organization, Dracunculiasis (Guinea-worm disease) Fact Sheet, https://www.who.int/news-room/fact-sheets/detail/dracunculiasis-(guinea-worm-disease)